Solar tracking reflector system for structure lighting

ABSTRACT

A solar tracking device is mounted above a skylight of a building. An array of mirrors is rotated at a rate of one revolution per day to reflect sunlight through the skylight. A control circuit intermittently adjusts the angular position of the tracking device so that the mirrors face the sun. A solar array charges an internal energy storage system so that no external power source is needed. The control circuit within the tracking device reduces the power requirements at night and when not moving the tracking device during the daytime to conserve electrical energy.

RELATED APPLICATIONS

The present application is a continuation of International ApplicationNo. PCT/US2007/069828, filed on May 27, 2007, which claims priority fromU.S. patent application Ser. No. 11/754,156, filed on May 25, 2007, andfrom U.S. Provisional Application No. 60/803,362, filed on May 27, 2006.U.S. patent application Ser. No. 11/754,156 claims the benefit ofpriority under 35 USC §119(e) to U.S. Provisional Application No.60/803,362, filed on May 27, 2006.

TECHNICAL FIELD

The present invention is in the field of building interior illuminationusing reflected sunlight through an opening in the roof (e.g., askylight).

BACKGROUND ART

Skylights provide natural sunlight to interior locations of a buildingthat receive little or no light via windows. Although passive skylightsare adequate in some situations, generally such skylights only providesufficient lighting when the sun is at or near its zenith. During thewinter months, the sun is so low in the southern sky (assuming thebuilding is in the northern hemisphere) that the lighting provided by askylight is not sufficient even when the sun is at its zenith.

Many mechanisms have been developed in response to the foregoingproblem. For example, U.S. Pat. Nos. 5,999,323 (Wood), 6,433,932 (Aokiet al.), 6,493,145 (Aoki et al.), and 6,801,361 (Aoki et al.) illustratea number of mechanisms for reflecting sunlight through a skylight toilluminate the interior of a building. The mechanisms include one ormore mirrors positioned at an angle with respect to vertical so thatwhen the sun is positioned low in the sky, the sunlight is reflecteddownward into the building. The mechanisms are motorized so that eachmirror faces the sun and tracks the apparent movement of the sun acrossthe sky. Thus, the light from the sun is reflected during the morningand the afternoon as well as during midday.

Although the known mechanisms provide advantages over passive skylights,the mechanisms include complicated structures and control mechanisms andthus tend to be unreliable and expensive to purchase, install andmaintain. A need continues to exist for a room-mounted solar trackingdevice that is reliable and inexpensive and that is simple to install,and that requires little or no maintenance.

DISCLOSURE OF THE INVENTION

A solar tracking device for mounting above a skylight of a buildingincludes a vertical support structure that receives the shaft of amotorized control head. The control head encloses control circuitry anda motor. A shaft extending from the control head is held in a fixedposition by the vertical support structure so that when the motoroperates, the frame of the motor rotates about the shaft along with thecontrol box. The rotation of the control box is controlled so that thecontrol box generally follows the apparent motion of the sun duringdaylight hours.

A mirror support structure supports a plurality of mirrors that arepositioned at an angle to reflect sunlight through the skylight. Themirror support structure is mechanically coupled to the control box androtates with the control box.

A solar array is also mechanically coupled to the control box and ispositioned to face the sun when the mirrors are positioned to face thesun. The solar array produces electrical power from solar energy. Theelectrical power is communicated to a storage system within the controlbox. The storage system provides electrical power to the controlcircuitry and thus to the motor. No external electrical power isprovided to the solar tracking device. The storage system stores asufficient amount of energy to maintain the operation of the solartracking device even if the sun is occluded for a number of successivedays. The storage system is replenished rapidly when the solar array isexposed to the sun.

In accordance with a first preferred embodiment, a solar tracking systemmountable above a skylight of a building includes a control box. Anelectrical motor within the control box drives the control box about ashaft that extends below the control box. A vertical support structureis positionable above a central portion of the skylight. The verticalsupport structure has an upper portion that receives the shaft extendingfrom the control box. A motion control circuit within the control boxcontrols the motor to cause the control box to rotate about the extendedshaft. A voltage supply circuit within the control box provideselectrical energy to the motion control circuit and the motor. A solararray mechanically and electrically coupled to the control box produceselectrical energy in response to sunlight and provides the electricalenergy to the voltage supply circuit within the control box sufficientto operate the control box without any other source of electricalenergy. Mirrors are coupled to the control box to rotate with thecontrol box. The mirrors are positioned at respective angles to reflectsunlight through the skylight into the building. In the illustratedembodiment of the solar tracking system, the motion control circuitintermittently rotates the control box during daytime hours to positionthe mirrors towards calculated positions of the sun. The motion controlcircuit rotates the control box at the end of a day to a calculatedposition of the sun at sunrise on the next following day. The motioncontrol circuit calculates the position of the azimuthal position of thesun based on the date and time of day and based on at least the latitudeand longitude position of the solar tracking system. In certainembodiments, the latitude and longitude position are permanently storedin a non-volatile memory within the motion control circuitry. In otherembodiments, the latitude and longitude position and the date and timeof day are obtained by accessing a global positioning receiverincorporated into the motion control circuitry.

In a particularly preferred embodiment, the voltage supply circuitcomprises first, second, third and fourth voltage generating circuits.The first voltage generating circuit comprises passive componentscoupled to the electrical output of the solar array to charge at least afirst storage capacitor to a variable voltage. The variable voltageacross the storage capacitor is limited to a maximum value by a firstvoltage limiting device. The second voltage generating circuit alsocomprises passive components coupled to the electrical output of thesolar array. The second voltage generating circuit comprises a secondvoltage limiting device to provide a limited output voltage. The limitedoutput voltage is provided to a common voltage node, which is coupled tothe power input terminals of digital devices in the motion controlcircuit. The third voltage generating circuit comprises a buck powersupply coupled to receive the variable voltage from the first voltagecircuit. The buck power supply produces a first constant voltage whenenabled by the motion control circuit. The first constant voltage isprovided as a power source for the electrical motor. The fourth voltagegenerating circuit comprises a boost power supply coupled to receive thefirst constant voltage. The boost power supply produces a secondconstant voltage when enabled by the motion control unit. The secondconstant voltage is provided to the common voltage node such the voltageat the common voltage node is the higher of the limited output voltagefrom the second voltage generating circuit or the second constantvoltage. A second storage capacitor is coupled to the common voltagenode to be charged by the higher of the limited output voltage from thesecond voltage generating circuit or the second constant voltage fromthe fourth voltage generating circuit. The second storage capacitorsupplies electrical energy to the common voltage node when the limitedoutput voltage and the second constant voltage are both less than thevoltage across the second storage capacitor. Preferably, the buck powersupply is selectively enabled by an enable signal from the motioncontrol circuit. The enable signal is maintained in an inactive stateuntil the motion control circuit receives a sufficient voltage from thefirst voltage generating circuit to be fully operational.

Preferably, the first storage capacitor is a super capacitor having acapacitance of at least 1 farad. Also preferably, the second storagecapacitor is a super capacitor.

In a second embodiment, the control box for the solar tracking systemhas an outer wall that is penetrated by at least two openings. The twoopenings are positioned on the outer wall such that one of the openingsfaces the sun when the angular position of the solar array and themirrors lags the apparent position of the sun by at least an angularamount. The other opening faces the sun when the angular position of thesolar array and the mirrors leads the apparent position of the sun by atleast approximately the same angular amount. At least one photodetectoris located within the control box. The photodetector is positioned withrespect to the two openings such that the photodetector is shaded by theouter wall when the solar array and the plurality of mirrors are facingthe sun. When shaded from sunlight, the photodetector is inactive. Thephotodetector receives sunlight and produces an output signal wheneither of the two openings is facing the sun. If one of the openings isfacing the sun, the angular position of the solar array and the mirrorsis either leading or lagging the angular position of the sun.Accordingly, the solar array produces less energy and the mirrors arenot reflecting a maximum quantity of sunlight. The control circuitryresponds to the output signal produced by the photodetector and adjuststhe rotation rate of the motor. The control circuitry temporarilyadjusts the rotation rate to rotate the control box until thephotodetector is no longer producing an output signal caused by lightthrough the opening that was facing the sun. The control circuitrycontinues to rotate the control box for a sufficient angular distance toexpose the photodetector to light through the other opening. If thephotodetector does not produce a signal when the control box has rotatedby the sufficient angular distance, then the other opening must belocated in the opposite angular direction. If the light from the secondopening is not detected by rotating in the original direction, thecontrol circuitry reverses the direction of rotation. After rotating bythe sufficient angular distance in the second direction, thephotodetector again detects the light through the first opening. Thecontrol circuitry continues rotating in the reverse direction at thehigher rotation rate until the photodetector detects the light throughthe second opening. When the photodetector detects the light through thesecond opening, the control system is able to determine whether theoriginal rotation rate was too fast or two slow. In particular, if thelight from the second opening is detected when rotating at the higherrotation rate in the original direction, the original rotation rate wastoo slow. Accordingly, the rotation rate needs to be increased. If thesecond opening is detected when rotating at the higher rotation rate inthe second direction, the original rotation rate was too fast.Accordingly, the rotation rate needs to be decreased.

Before adjusting the rotation rate, the control circuitry in the secondembodiment first returns the control box to a position where thephotodetector is shaded from sunlight and where the solar array and themirrors are facing the sun. The control circuitry is able to determinethe direction and angular distance to rotate the control box because theprevious operations have identified which opening is allowing light toimpinge on the photodetector. The angular distance traveled between theangular positions where the photodetector is active is also known.Accordingly, the control circuitry moves the control box by an angulardistance of approximately one-half the angular distance between the twoactive positions.

In preferred implementations of the second embodiment, the controlcircuitry increases or decreases the original rotation rate by aspecific amount each time the control circuitry performs the foregoingoperations. In preferred implementations, the control circuitry variesthe magnitude of the change of the rotation rate in accordance with thetime lapsed since the previous adjustment. Thus, the control systemgradually adjusts the rotation rate to closely match the apparent rateof movement of the sun.

The control circuitry of the second embodiment, adapts to a newinstallation by rotating the control box at a higher rate when initiallyinstalled until the light through each opening is detected by thephotodetector. The control circuitry determines from the times at whichthe photodetector produces the output signal whether the system isinstalled in the northern hemisphere or the southern hemisphere. Thecontrol circuit selects the normal direction of rotation in accordancewith the location where the system is installed.

BRIEF DESCRIPTION OF THE DRAWINGS

Certain embodiments in accordance with the present invention aredescribed below in connection with the accompanying drawing figures inwhich:

FIG. 1 illustrates one embodiment of a solar tracking system comprisinga support structure, a rotating control box, a solar array thatgenerates power, a mirror support beam, and a plurality of mirrors;

FIG. 2 illustrates an elevational view of the solar tracking system ofFIG. 1;

FIG. 3 illustrates an enlarged cross-sectional elevational view of thecontrol box and a portion of the mirror support beam of FIG. 1;

FIG. 4 illustrates cross-sectional plan view of the control box of FIG.1;

FIG. 5 illustrates an enlarged partial cross-sectional elevational viewof the vertical support structure and the motor shaft of FIG. 1;

FIG. 6 illustrates a block diagram of the electrical circuitry of thecontrol box of FIG. 1;

FIGS. 7A, 7B and 7C illustrate the effect of fast or slow rotation onthe light sensed by the internal photodetector in the embodiment of FIG.1, wherein FIG. 7A illustrates the rotating control box properlysynchronized with the solar position, FIG. 7B illustrates the rotatingcontrol box in a position caused by rotating too fast, and FIG. 7Cillustrates the rotating control box in a position caused by rotatingtoo slowly;

FIG. 8 illustrates a flow chart of the operation of the electricalcircuitry of FIG. 6 to correct the rotation rate;

FIG. 9 illustrates a flow chart of the operation of the electricalcircuitry of FIG. 6 at startup to determine the hemisphere where thesystem is installed;

FIG. 10 illustrates a flow chart of the operation of the electricalcircuitry of FIG. 6 in response to the level of charge of the powerstorage unit less than a predetermined level;

FIG. 11 illustrates the solar tracking system of FIG. 1 mounted on apair of beams (shown in partial cross section) proximate a skylight witha transparent protective dome (shown in phantom) in position over thesolar tracking system;

FIG. 12 illustrates a perspective view of a second embodiment inaccordance with additional aspects of the present invention;

FIG. 13 illustrates a partially exploded perspective view of theembodiment of FIG. 12;

FIG. 14 illustrates an enlarged perspective view of the embodiment ofFIGS. 12 and 13 further exploded to show the mounting of the controlhead shaft in the support post;

FIG. 15 illustrates a top plan view of the control head of FIGS. 12-14partially broken away to show the internal motor and gearingarrangement;

FIG. 16 illustrates an exploded perspective view of the control headgenerally looking from above the control head;

FIG. 17 illustrates an exploded perspective view of the control headgenerally looking from below the control head;

FIG. 18 illustrates a cross-sectional view of the control head takenalong the lines 18-18 in FIG. 15;

FIG. 19 illustrates a schematic block diagram of the electroniccircuitry on the circuit board within the control head of FIGS. 12-17;

FIG. 20 (comprising FIGS. 20A and 20B) illustrates a main operationalroutine that is executed when the control processor of FIG. 19 isinitially started from a reset condition;

FIG. 21 (comprising FIGS. 21A, 21B, 21C and 21D) illustrates themovement control routine that is called by the main routine of FIG. 20;and

FIG. 22 illustrates the power down routine that is activated by the mainroutine of FIG. 20 and the movement control routine of FIG. 21.

MODES FOR CARRYING OUT THE INVENTION

FIGS. 1-6 illustrate an embodiment of a solar tracking system 100. Thesolar tracking system includes a support structure 110, which comprisesa vertical tube 112 mounted at the approximate midpoint of a horizontalbeam 114. The beam includes a first mounting bracket 116 at one end anda second mounting bracket 118 at an opposite end. The mounting bracketsare spaced apart by a distance corresponding to a distance across aconventional building skylight. Shorter or longer horizontal beams canbe used for smaller or larger skylights. The support structure supportsa control box 120 via a motor shaft 122 that extends vertically from thebottom of the control box. The lower end of the motor shaft is insertedinto the upper end of the vertical tube as shown in FIG. 5. As shown incross section in FIG. 3, a motor 124 within the control box causes thecontrol box to rotate about a centerline 126 defined by the motor shaft.

A solar array 130 is coupled to the control box and rotates with thecontrol box. As described below, the solar array generates electricalpower for control circuitry and a drive motor. The electrical energyfrom the solar array is stored in an energy storage unit 132 shown inFIGS. 3 and 4.

A mirror support beam 140 is coupled to the control box and also rotateswith the control box. A plurality of mirrors comprising a first mirror150, a second mirror 152 and a third mirror 154 are supported by themirror support beam. In the illustrated embodiment, the three mirrorsare formed as generally planar surfaces; however, in alternativeembodiments (not shown), the three mirrors may have mildly curvedsurfaces. In the following discussion, references to the planar surfacesof the mirrors should be understood to encompass the mildly curvedsurfaces of the alternative embodiments.

In the illustrated embodiment, the support beam 140 has a firstgenerally horizontal portion 142 that is positioned below the controlbox 120 and extends rearward from the control box. In this description,“frontward” is defined as the peripheral portion of the control box inthe direction toward the solar array 130 (to the right in FIG. 2), and“rearward” is defined in the opposite direction (to the left in FIG. 2).When the control box rotates, the first portion rotates in a horizontalplane (not shown). The support beam has a second portion 144 thatextends frontward from the first portion and is disposed downwardly atan angle of approximately 20-25 degrees with respect to the horizontalplane in which the first portion rotates.

The first mirror 150 is disposed on the first portion 142 of the supportbeam 140 and is proximate the rearmost portion of the support beam. Inthe illustrated embodiment, an upper portion (e.g., approximatelyone-third of the height) of the first mirror extends above the supportbeam to an upper edge 160 and a lower portion (e.g., approximatelytwo-thirds of the height) of the first mirror extends below the supportbeam to a lower edge 162. The relative sizes of the two portions of thefirst mirror are illustrative only and are not intended to be limiting.

The first mirror has a front surface 164 facing toward the control box120 and has an opposite rear surface 166. The front surface is highlypolished or coated to provide to cause the front surface to be highlyreflective. The thickness of the first mirror between the front surfaceand the rear surface is selected to provide a sufficient strengthwithout being overly heavy. For example, in the illustrated embodiment,the first mirror advantageously comprises aluminum or other suitablematerial having a thickness of approximately 2-10 millimeters.

In the illustrated embodiment, the first mirror 150 includes a hole 170sized to allow the first portion 142 of the support beam 140 to passthrough the mirror. The first mirror includes a first generallyhorizontal reinforcing strap 172 disposed across the rear surface belowthe hole 170. A second generally horizontal reinforcing strap 174 isdisposed on the front surface proximate the lower edge 162. A shorterthird horizontal reinforcing strap 176 is advantageously positioned onthe front surface just below the hole. A mounting bracket 178 (FIG. 2)is mounted to the rear surface of the mirror below the hole injuxtaposition to the third reinforcing strap. The three reinforcingstraps and the mounting bracket are attached to the first mirror by aplurality of suitable fasteners (e.g., rivets, screws, or the like)which pass through the thickness of the first mirror. As shown in FIG.2, the mounting bracket is secured to the first portion of the supportbeam, which extends through the hole.

As shown more clearly in the elevational view of FIG. 2, the firstmirror 150 is disposed at an angle of approximately 20-25 degrees withrespect to vertical such that the lower edge 162 is farther from thecenterline 126 than the upper edge 160. A cable 180 extends downwardlyfrom the rearmost portion of the first portion 142 of the support beam140 to the lower edge of the first mirror to provide additional supportto maintain the first mirror at the desired angle. The lowermost end ofthe cable is secured to the second reinforcing strap 174 through thethickness of the first mirror.

The second mirror 152 and the third mirror 154 are supported by thesecond portion 144 of the support beam 140. As illustrated, the secondand third mirrors are each generally perpendicular to the second portionof the support beam. Since the second support beam is disposed at anangle of 20-25 degrees with respect to the horizontal plane, the firstand second mirrors are disposed at respective angles of 20-25 degreeswith respect to vertical. Thus, the second and third mirrors aregenerally parallel to the first mirror 150 in the illustratedembodiment. In alternative embodiments (not shown), the three mirrorscan be disposed at different angles with respect to vertical.

The second mirror 152 is positioned on the second portion 144 of thesupport beam 140 close to the juncture of the second portion with thefirst portion 142. The second mirror has a reflective front surface 190and a rear surface 192, which are disposed between an upper edge 194 anda lower edge 196. The lower edge is closer to the centerline 126 thanthe upper edge. The rear surface faces toward the control box 120, andthe front surface faces away from the control box.

A first generally horizontal reinforcing strap 200 extends across therear surface 192 of the second mirror 152 proximate the upper edge 194.A second reinforcing generally horizontal reinforcing strap 202 extendsacross the front surface 190 proximate the lower edge 196. The upperedge 194 is attached to the second portion 144 of the support beam 140by a mounting bracket 204, which is disposed on the front surface of themirror opposite the first reinforcing strap. The reinforcing straps andthe mounting bracket are attached to the second mirror by a plurality ofsuitable fasteners (e.g., rivets, screws, or the like) which passthrough the thickness of the second mirror. A cable 208 extendsdownwardly from a forwardmost portion of the first portion 142 of thesupport beam to the lower edge of the second mirror to provideadditional support to maintain the second mirror at the desired angle.The cable 208 is secured to the second reinforcing strap through thethickness of the mirror.

The third mirror 154 is positioned on the second portion 144 of thesupport beam 140 proximate a forwardmost end of the second portion. Thethird mirror has a reflective front surface 220 and a rear surface 222,which are disposed between an upper edge 224 and a lower edge 226. Thelower edge is closer to the centerline 126 than the upper edge. The rearsurface faces toward the control box 120, and the front surface facesaway from the control box.

A first generally horizontal reinforcing strap 230 extends across therear surface 222 of the third mirror 154 proximate the upper edge 224. Asecond reinforcing generally horizontal reinforcing strap 232 extendsacross the front surface 220 proximate the lower edge 226. The upperedge 224 is attached to the second portion 144 of the support beam 140by a mounting bracket 234, which is disposed on the front surface of themirror opposite the first reinforcing strap. The reinforcing straps andthe mounting bracket are attached to the third mirror by a plurality ofsuitable fasteners (e.g., rivets, screws, or the like) which passthrough the thickness of the second mirror. A cable 238 extendsdownwardly from the second portion of the support beam at a position onthe second portion between the second mirror 152 and the third mirror.The cable 238 extends to the lower edge of the third mirror to provideadditional support to maintain the third mirror at the desired angle.The cable 238 is secured to the second reinforcing strap through thethickness of the mirror. The angles of the mirror can be adjusted duringinstallation.

As illustrated in FIG. 2, the angle of the second portion 144 of themirror support beam 140 causes the upper edge 194 of the second mirror152 to be substantially lower than the upper edge 160 of the firstmirror 150. Thus, a substantial portion of the area of the front surfaceof the first mirror is exposed to sunlight even when the sunlightimpinging on the mirrors is arriving at a small angle to a horizontalplane. Similarly, the upper edge 224 of the third mirror 154 is lowerthan the upper edge of the second mirror so that a substantial portionof the area of the front surface of the second mirror is exposed tosunlight when the sunlight arrives at a small angle to the horizontalplane.

The solar array 150 extends forwardly from the control box 120 and iscoupled to the control box by a generally horizontal hollow supportstructure 250. In the illustrated embodiment, the hollow supportstructure comprises a cylindrical tube. The solar array produceselectrical power at a voltage in a range of 10-20 volts. As shown in thecross-sectional illustrations in FIGS. 3 and 4, the electrical power iscoupled to a circuit board 252 via a plurality of power wires 254. Asfurther illustrated in FIGS. 3 and 4, the circuit board includes theelectrical energy storage device 132. In the preferred embodiment, theenergy storage device is a super-capacitor, which stores a sufficientcharge to operate the electrical control circuitry and the motor 124 forat least 15 days in the absence of sufficient sunlight to enable thesolar array to recharge the storage device.

As shown in the cross-sectional view of FIGS. 3 and 4, the control box120 includes an upper portion 270 and a lower portion 272. The motor 124is located in the lower portion and is secured to the control box by amounting bracket 274. In the illustrated embodiment, the motor iscontrolled at a uniform rate by motor control circuitry 276 representedby an integrated circuit on the circuit board 252. The motor is coupledto the circuit board by a plurality of wires 278. The motor includes themotor shaft 122 that extends downwardly through an opening in the bottomof the control box and further extends through an opening in the firstportion 142 of the support beam 140. The lower portion of the controlbox is secured to the support beam by suitable fasteners, such as, forexample a pair of machine screws 282 illustrated in FIG. 3.

In FIG. 3, the motor 124 is illustrated as a basic motor that drives themotor shaft 122 directly. It should be understood that the motor mayadvantageously include an internal gear assembly (not shown) thatreduces the rotation rate of the motor by a suitable ratio to obtain thedesired rotation rate of one revolution per day at the motor shaft.

As shown in FIGS. 1 and 4, the upper portion 270 of the control box 120includes a first opening 300 and a second opening 302, which aredisposed on opposite sides of a horizontal system centerline 304 (FIG.4) that is parallel to the support beam 140 and the hollow supportstructure 250. In the illustrated embodiment, the respective centers ofthe two openings are disposed on respective centerlines 306 and 308emanating from the center of the control box at respective angles ofapproximately 15 degrees with respect to the system centerline. Thus,the centerlines of the two openings are approximately 30 degrees apartin angular distance. As further shown in FIGS. 3 and 4, a photodetector310 is mounted on the circuit board 252 at a location approximately onthe system centerline. As illustrated in more detail in connection withFIGS. 7A, 7B and 7C, the position of the photodetector with respect tothe openings causes the photodetector to be shaded from sunlight whenthe system centerline is directed toward the sun. On the other hand,when the centerline of one of the openings is directed toward the sun,the photodetector is exposed to sunlight. The operation of the controlcircuitry in response to the exposure of the photodetector is alsodiscussed below in connection with FIGS. 7A, 7B and 7C.

FIG. 5 illustrates an enlarged partial cross-sectional elevational viewof the vertical support structure 110 and the motor shaft 122 of FIG. 1.The vertical support structure comprises the hollow tube or pipe 112that is mounted on the generally horizontal beam 114. As shown in FIG.1, the beam extends between the first mounting bracket 116 and thesecond mounting bracket 118 shown in FIG. 1 and in FIG. 11. As describedbelow with respect to FIG. 11, when the solar tracking system 100 isinstalled on a roof over a skylight, the mounting brackets are securedto structural support members proximate the skylight. As shown in thecross-sectional view of FIG. 5, the hollow tube is secured to themidpoint of the beam in a suitable manner. For example, in theillustrated embodiment, the hollow tube includes a fixed collar 364proximate a threaded lower portion 366. The threaded lower portion isinserted through a hole 368 in the beam and secured by a washer 370 anda nut 372. In another embodiment (not shown), the hollow tube may bepermanently welded to the beam.

The upper portion of the hollow tube 112 receives the lower end of themotor shaft 122. The inside diameter of the hollow tube is sized toprovide a snug fit with the outside diameter of the motor shaft. Acotter pin 374 or other generally horizontal device is inserted throughthe hollow tube at a selected location to provide a support for the endof the motor shaft to maintain the motor shaft at a fixed verticalposition in the hollow tube. The vertical position of the shaft in thehollow tube is determined by the length of the motor shaft, the heightof the hollow tube and the desired height of the mirrors above thehorizontal beam 352.

In view of the foregoing description of the structure of the solartracking system, it should be understood that when the motor 124 isoperated, the shaft 280 turns relative to the motor and the control box120. However, since the shaft 280 is confined by the snug engagementwith the hollow tube 350, the shaft is unable to turn with respect tothe vertical support structure 110. Rather, the relative rotation of themotor shaft and the motor causes the motor and the attached control boxto rotate with respect to the vertical support structure. As discussedabove, the rotation rate is controlled by control circuitry on thecircuit board 252 so that the control box completes one revolution perday (e.g., 360 angular degrees per day). Thus, the relative rotation ofthe motor shaft and the motor is 15 degrees per hour or 1 degree every 4minutes.

FIG. 6 illustrates a block diagram 600 of the electrical circuitry ofthe control box of FIG. 1. The electrical circuitry includes the motor124, the solar array 130, the electrical energy storage device 132, andthe photodetector 310 that were discussed above. The electricalcircuitry further includes the motor control circuitry 276, whichreceives control signals from a system control circuit 610. The motorcontrol circuitry is responsive to the control signals from the systemcontrol circuit 610 to selectively apply power from the electricalenergy storage device to the windings of the motor to cause the motor torotate (e.g., step) by a predetermined angular distance. The electricalcircuitry further includes a power control circuit 620 that receives theelectrical power produced by the solar array, conditions the power, andselectively applies the power to charge the energy storage device. Thepower control circuit further monitors the energy stored in the energystorage device to determine when the charge is less than a predeterminedlower limit and to provide a low-power level signal to the systemcontrol circuit to indicate that the charge is less than the lowerlimit.

The system control circuit 610 is responsive to the signal from thepower control circuit 620 and responsive to the signal produced by thephotodetector 310 when the photodetector is activated by sunlight. Whenthe system control circuit receives the low-power level signal from thepower control circuit that indicates that the energy stored in theenergy storage device is less than the predetermined level, the controlcircuit performs a fail-safe routine (described below) to rotate thecontrol box 120 to a predetermined location and to stop all rotationuntil the power control circuit deactivates the low-power level signal.

The system control circuit 610 is responsive to the signal from thephotodetector 310 to adjust the position of the control box 120 so thatthe solar array 130 and the mirrors 150, 152, 154 are facing the sun andso that the photodetector is shaded from sunlight. The operation of thesystem control circuit is illustrated by the partial plancross-sectional views in FIGS. 7A, 7B and 7C and by the flow diagrams inFIG. 8. In particular, FIGS. 7A, 7B and 7C illustrate the effect of fastor slow rotation on the light sensed by the internal photodetector. FIG.7A illustrates the rotating control box properly synchronized with thesolar position. As illustrated in FIG. 7A, the control box 120 is facingthe sun so that the sunlight (represented by a plurality of phantomlines) passes through the first opening 300 and through the secondopening 302. The photodetector 310 is positioned directly behind theportion of the wall of the control box between the two openings and isshaded from the sunlight passing through both openings. Thephotodetector is shaded from sunlight during most of the day and is onlyactive for short durations while the system is performing the correctionoperations described below. Thus, the rate of any degradation of thephotodetector that may be caused by exposure to intense sunlight issubstantially reduced because of the short exposure times.

FIG. 7B illustrates the rotating control box in a position caused byrotating too fast. In particular, the control box has advanced to anangular position approximately 15 degrees ahead of the angular positionof the sun such that the first opening 300 is generally facing towardthe sun. Thus, the sunlight passing through the first opening impingesdirectly on the photodetector 310 and cause the photodetector to beactive. The active photodetector activates the photodetector signal tothe system control unit 610 to indicate that the control box is nolonger correctly positioned. The response of the system control unit tothe active photodetector signal is described below.

FIG. 7C illustrates the rotating control box in a position caused byrotating too slowly. In particular, the control box has regressed toangular position approximately 15 degrees behind the angular position ofthe sun such that the second opening 302 is generally facing toward thesun. Thus, the sunlight passing through the second opening impingesdirectly on the photodetector 310 and cause the photodetector to beactive. The active photodetector activates the photodetector signal tothe system control unit 610 to indicate that the control box is nolonger correctly positioned. The response of the system control unit tothis active photodetector signal is described below.

As indicated above, sunlight impinging on the photodetector 310 througheither the first opening 300 or the second opening 302 causes thephotodetector to provide an active photodetector signal to the controlunit 610. Although the active photodetector signal indicates that one ofthe openings is facing the sun, the active photodetector signal does notindicate which of the two openings if facing the sun. Thus, the systemcontrol unit initiates a search routine 800 illustrated in FIG. 8.

The search routine 800 begins in a block 810 wherein the system controlunit increases the angular rotation rate of the motor 124 by sending acontrol signal to the motor control circuitry 276. For example, therotation rate may be advantageously increased from one revolution perday to one revolution per hour.

The system control unit initially assumes that the original rotationrate of the motor was too slow and that the light impinging on thephotodetector 310 is passing through the second opening 302, asillustrated in FIG. 7C. Thus, the increased rotation rate will cause thecontrol box to advance relatively rapidly so that the sunlight is firstblocked by the outer wall of the control box between the two openings.The system control unit waits in a block 812 until the photodetectorbecomes inactive, and the enters a decision sequence comprising a firstdecision block 814, which checks to determine whether the photodetectorsignal has again become active. If the photodetector signal is active,the system control unit sets a “slow” status flag and proceeds to aprocedure block 816, which is described below. If the photodetectorsignal is not yet active, the system control unit checks whether themotor has rotated more than 30 degrees in a decision block 818. If themotor has not rotated 30 degrees, the system control unit returns to thedecision block 814 and continues checking.

If the motor 124 has rotated 30 degrees without the photodetector signalbecoming active, the control box 120 is rotating in the wrong direction.Accordingly, the original opening that was passing the sunlight to thephotodetector 310 was not the first opening 300 as assumed. Rather, thesunlight must have been passing through the second opening 302 as shownin FIG. 9C. Thus, the system control unit proceeds from the decisionblock 818 to a block 820 wherein the system control unit issues acontrol signal to the motor control circuitry 276 to cause the motorcontrol circuitry to reverse the rotation direction of the motor andstart moving the control box in the original rotation direction towardthe second opening.

After initiating the rotation in the original direction, the systemcontrol unit 810 proceeds to a block 822 to rotate the motor 124 for 30degrees in the new direction so that the photodetector signal is againactive because of the sunlight passing through the second opening 302 inthe control box 120. The system control unit then waits in a block 824for the photodetector to deactivate the photodetector signal. When thesystem control unit detects the deactivation of the photodetectorsignal, the system control unit proceeds to a decision sequence to waitfor the photodetector to detect sunlight through the first opening 300.

In a decision block 830, the system control unit 610 checks to determinewhether the photodetector signal has again become active. If thephotodetector signal is active, the system control unit sets a “fast”status flag and proceeds to the procedure block 816, which is describedbelow. If the photodetector signal is not yet active, the system controlunit checks whether the motor 124 has rotated more than 30 degrees in adecision block 832. If the motor has not rotated 30 degrees, the systemcontrol unit returns to the decision block 830 and continues checking.If the motor rotates 30 degrees without the photodetector signalbecoming active, the system control unit proceeds from the decisionblock 832 to an alarm block 834. The alarm block 834 advantageouslycomprises routines to recover from this condition, which should notoccur during normal operations. Since the sunlight may be occluded byheavy clouds during the foregoing routine, in one embodiment, the systemcontrol unit waits a predetermined time and then resumes the searchforegoing search routine with a broader angular search range.

When the system control unit 610 enters the procedure block 816, thesystem control unit knows which opening is currently facing the sun andknows the direction in which to rotate the control box 120 so that theportion of the wall between the two openings faces the sun and shadesthe photodetector 310 as illustrated in FIG. 7A. According, the systemcontrol unit sends a signal to the motor control circuitry 276 to causethe motor 124 to rotate approximately 15 degrees in the correctdirection. The system control unit then sends a signal to the motorcontrol circuitry to adjust the original rotation rate to a slowerrotation rate if the “fast” status signal is set or to a faster rotationrate if the “slow” status signal is set. The system control unit thenwaits for the photodetector signal to become active before againperforming the foregoing routine.

FIG. 9 illustrates an automatic system startup routine 850. The systemcontrol circuit 610 is preprogrammed with an initial rotation speed thatis reasonably close to the expected rotation speed required to properlytrack the apparent movement of the sun; however, the directions of theapparent movement of the sun in the southern hemisphere and the northernhemisphere are opposite each other. Thus, the system control circuitmust determine which direction is the proper rotation direction when thesystem is first installed. Accordingly, system control circuit receivesa third status flag identified as the “startup” flag. The startup flagis set whenever power is initially applied to the system, either atinitial installation or when sunlight is blocked by clouds or othercauses for a sufficient time to completely deplete the energy in theenergy storage unit 132.

In a block 852 and a block 854, the system control circuit firstpositions the control box 120 so that the photodetector 310 is shadedfrom sunlight in accordance with the movements described in connectionwith FIG. 8. In particular, in the block 852, the system control circuitsends control signals to the motor control circuitry 276 and monitorsthe output signal from the photodetector to locate the first opening 300and the second opening 302. Then, in the block 854, the system controlcircuitry sends control signals to the motor control circuit to move thecontrol box to a position where a point midway between the two openingsis facing the sun and then stop in that position.

In a block 856, the system control circuit waits for approximately onehour (corresponding to an angular movement of 15 degrees) for theapparent movement of the sun to cause sunlight to pass through one ofthe openings. Then, in a block 858, the system control circuit performssteps similar to the steps described above to identify the openingthrough which the sunlight passed to impinge on the photodetector. Ifthe system control unit determines that the sunlight passed through thesecond opening, the system control unit determines that the solartracking system is located in the northern hemisphere. Thus, in a block860, the system control circuit sends a control signal to the motorcontrol circuitry to activate clockwise rotation of the control box. Ifthe system control unit determines that the sunlight passed through thefirst opening, the system control unit determines that the solartracking system is located in the southern hemisphere. Thus, in a block862, the system control circuit sends a control signal to the motorcontrol circuitry to activate counterclockwise rotation of the controlbox.

FIG. 10 illustrates a routine 900 that is performed when the powercontrol circuit 620 activates the signal to the system control circuit610 to indicate that the stored energy is less than the predeterminedlimit. The power control circuit also provides a signal to the systemcontrol circuit to indicate when the solar array 130 is activelyproducing electrical energy. The system control circuit includes atiming circuit that enables the system control unit to track the currentangular location of the control box 120. Thus, the system controlcircuit is able to identify and store the angular locations thatcorrespond to the sunrise and sunset of the last day when sufficientsunlight was available to enable the solar array to produce electricalenergy. It should be understood that the system control circuit does notstore angular locations that correspond to a significantly shorter rangeof daylight than for a previously stored day since the angular positionsof the sunrises and sunsets do not differ greatly from day to day. Asignificant change in the angular location of the control box at sunriseor sunset of the current day may indicate significant cloud cover thatblocks sufficient light from reaching the solar array.

When the system control circuit 610 receives the low-energy signal fromthe power control circuit 620, the system control circuit performs aroutine in a block 902 to retrieve the locations of the control box 120at the previous sunrise and the previous sunset beginning and the end ofthe last solar day. Then, in a block 904, the system control unitcalculates the location of the control box at midday of the last solarday. In a block 906, the system control circuit calculates the angularmovement required to advance the control box so that the solar arrayfaces the sun at the calculated midday location. In a block 908, thesystem control unit then issues a control signal to the motor controlunit 276 to cause the motor 124 to rotate by the required angularmovement and then stop. In a decision block 910, the system control unitwaits until the low-energy level signal is deactivated by the powercontrol circuit. During a day with a moderate amount of sunlight (e.g.,scattered or no clouds), the solar array 130 rapidly charges the energystorage device 132 to a sufficient energy level to resume normaloperations wherein the solar array continues to charge the energystorage device as the rotation of the control box tracks the apparentmovement of the sun. Thus, the system control circuit advances to ablock 912 wherein the system control unit sends a control signal to themotor control circuitry 276 to cause the motor control circuitry toactivate the motor 124. More particularly, the system control circuitperforms the startup routine 850 described above to assure that thecontrol box 120 is rotated in the proper direction and to assure thatthe photodetector 310 is positioned in the shaded area behind theportion of the control box wall between the two openings 300, 302.

FIG. 11 illustrates the solar tracking system 100 of FIG. 1 mounted on apair of beams 950, 952 (shown in partial cross section) proximate askylight 960. A transparent protective dome 970 (shown in phantom) ismounted over the solar tracking system to protect the solar trackingsystem from weather conditions. Unlike certain systems known in the art,the protective dome only has to be self-supporting and does not provideany structural support for the solar tracking system, which is mounteddirectly to the beams or to other sturdy structures.

FIGS. 12-22 illustrate an embodiment of a solar tracking system 1000 inaccordance with further aspects of invention. The solar tracking system1000 is similar to the solar tracking system 100 described above, andmany elements corresponding to previously described elements are notdescribed in detail in the following paragraphs.

As shown in FIGS. 12 and 13, the solar tracking system 1000 is mountedon a roof (not shown) of a structure (not shown) on a structural frame1010 formed of structural materials (e.g., wood, metal, or the like).For example, the structural frame advantageously comprises a generallyrectangular (e.g., square) frame around an opening in the roof. Thestructural frame 1010 forms a fixed opening in the roof of thestructure. The structural frame may also support a transparent panel1012 at a lower portion thereof to provide a lower cover over theopening in the roof prior to installation of the solar tracking system.After installation, the transparent panel may also serve to isolate thesolar tracking system from the interior environment of the structure onwhich the system is mounted.

The solar tracking system 1000 is positioned beneath a generallytransparent protective dome 1020, which is sized and shaped to conformto the size and shape of the frame 1010. As shown in more detail in FIG.13, the dome includes a peripheral mounting flange 1022 that issandwiched between a lower mounting frame 1024 and an upper mountingframe 1026. In the illustrated embodiment, the lower mounting frame issecured to the structural frame by suitable fasteners (e.g., screws,nails or the like). The mounting flange rests on the lower mountingframe 1024, and the upper mounting frame is placed over the mountingflange and is secured to the lower mounting frame to securely retain thedome. The interfaces between the upper mounting frame and the mountingflange are sealed so that any moisture or other contaminants falling onthe dome flow over the upper mounting frame and are blocked fromentering the volume formed between the inner surface of the dome and thetransparent panel 1012.

The solar tracking system 1000 is supported by a support assembly 1030.The support assembly comprises a support beam 1032 that is secured toinner walls of the structural frame 1010 by a pair of mounting brackets1034 at each end (only one of the mounting brackets can be seen in FIGS.12 and 13). The mounting brackets are secured to the structural frame bysuitable fasteners (e.g., screws, nails, or the like).

A support post 1040 extends substantially vertically from theapproximate midpoint of the support beam 1032. In the illustratedembodiment, the support post is mounted perpendicular to the supportbeam, which is mounted substantially horizontally on a flat roof (notshown). Preferably, if the solar tracking system 1000 is mounted on asloped roof (not shown), the structural frame 1010 is constructed toprovide a generally horizontal mounting reference for the support beam.Alternatively, the brackets at each end of the support beam areselectively positionable to maintain the support beam in a horizontalposition. In certain embodiments, the support post may be mounted at anangle to the support beam to compensate for the beam being in anon-horizontal position.

As shown in FIG. 14, at least an upper end of the support post 1040 ishollow. For example, in one embodiment, the inside dimensions of thesupport post are approximately 0.75 inch by 0.75 inch. The hollow upperportion of the support post receives a shaft 1062 that extends from acontrol head 1060. The outer diameter of the shaft is approximately 0.32inch. The portion of the shaft extending into the support post has aflat face 1064 formed thereon so that the extended portion of the shaftis generally “D” shaped. An adapter bushing 1066 is positioned into thesupport post. The adapter bushing has lower outside dimensions sized tofit within the support post and has upper outside dimensions to form aflange that rests on top of the support post. The adapter bushing has aninner bore that is sized and shaped to receive the extended portion ofthe shaft. Accordingly, the shaft is precluded from rotating withrespect to the support post. In alternative embodiments, the supportpost is advantageously manufactured of an extruded plastic material withthe upper portion having inside dimensions to receive and secure theshaft without using an adapter bushing.

The control head 1060 comprises a lower body portion 1070 and an upperremovable cap 1072. A mirror support beam 1100 is secured to the bottomof the lower body portion of the control head in a manner similar tothat described above with respect to the embodiment of FIGS. 1-11. Themirror support beam supports a first mirror 1110 via a first mountingbracket 1112, supports a second mirror 1114 via a second mountingbracket 1116, and supports a third mirror 1118 via a third mountingbracket 1120. The first mirror, the second mirror and the third mirrorgenerally correspond to the first mirror 150, the second mirror 152 andthe third mirror 154, respectively, in the previously describedembodiment.

In the illustrated embodiment, a rear portion of the mirror support beam1100 is generally horizontal and supports the first mirror 1110 at anangle of approximately 20 degrees with respect to vertical. The firstmirror has overall dimensions of approximately 31.5 inches by 31.5inches. The first mirror has lower rounded corners with radii ofapproximately 4 inches and upper rounded corners with radii ofapproximately 11 inches. The first mirror also has a cutout 1122 toaccommodate the passage of the mirror support beam therethrough.Accordingly, the first mirror has an overall reflective surface area ofapproximately 528 square inches. (Reductions in reflective surface areacaused by the first mounting bracket 1112 and the shadowing effect ofother elements are not considered in this approximation.)

The forward portion of the mirror support beam 1100 is angled downwardat an angle of approximately 45 degrees with respect to horizontal. Thesecond mirror 1114 and the third mirror 1118 are mounted generallyperpendicularly with respect to the forward portion of the mirrorsupport beam and are thus mounted at an angle of approximately 45degrees with respect to vertical.

The second mirror 1114 has a height of approximately 10.15 inches, has alower edge with a width of approximately 38.37 inches and an upper edgewith a width of approximately 33 inches. The upper and lower edges ofthe second mirror are connected by side edges having radii of curvatureof approximately 9.8 inches. The second mirror has a cutout 1124 toaccommodate the support post 1040. Accordingly, the second mirror has anoverall reflective surface of approximately 379 square inches.(Reductions in reflective surface area caused by the second mountingbracket 1116 and the shadowing effect of other elements are notconsidered in this approximation.)

The third mirror 1118 has a height of approximately 6.3 inches, has alower edge with a width of approximately 33.3 inches and an upper edgewith a width of approximately 30.5 inches. The upper and lower edges ofthe third mirror are connected by side edges having radii of curvatureof approximately 7.05 inches. Accordingly, the third mirror has anoverall reflective surface of approximately 132 square inches. (Thereduction in reflective surface area caused by the third mountingbracket 1120 is not considered in this approximation.)

In the embodiment illustrated in FIGS. 12 and 13, the three mirrors1110, 1114, 1118 comprise aluminum having a thickness of approximately0.05 inch. Approximately 0.5 inch of the lower edge of each mirror isbent at approximately 90 degrees to preclude bowing of the mirrorsurface in the horizontal direction. The strength and thickness of eachmirror is sufficient that no supporting wires are needed for theillustrated embodiment.

The control head 1060 is similar to the control box 120 of the previousembodiment. The lower body portion 1070 of the control head supports aphotovoltaic (solar) array 1200, which is generally aligned with themirror support beam 1100. The solar array is mounted in a solar panelsupport frame 1202 that is mechanically connected to the lower bodyportion of the control head by a deformable tab 1204. Preferably, thelower body portion, the deformable tab and the solar panel support frameare formed as a single unit by injection molding a suitable plastic. Thedeformable tab is then bent to position the solar panel support frame ata suitable angle to direct the solar array toward the sun. For example,in one embodiment, the solar panel support frame is positioned at anangle of approximately 45 degrees with respect to horizontal. The solarpanel is secured in the solar panel support frame by an upper framemember 1206 that latches onto the support frame.

FIGS. 15, 16, 17 and 18 illustrate additional details of the controlhead 1060. The control head is hollow and houses a DC motor 1300 that iselectrically connected via a first pair of conductors 1302, 1304 and afirst connector 1306 to a circuit board 1310. The circuit board iselectrically connected via a second connector 1312 and a second pair ofconductors 1314, 1316 to the solar array 1200.

In the illustrated embodiment, the motor 1300 comprises, for example, anFF-N30VB-0921 DC motor commercially available from Mabuchi Motor Co.,Ltd., of Matsudo City, Chiba, Japan. that rotates a motor output shaftat approximately 4200 revolutions per minute when powered with a DCvoltage of approximately 2.5 volts. The motor is positioned proximate tothe inner periphery of the control head 1060 and is mechanically coupledby a gear train 1320 to an upper portion of the shaft 1062, whichextends into the control head. The gear train advantageously comprises a12-tooth gear A on the output shaft of the motor 1300. A first compoundgear B has a 60-tooth upper gear that engages the 12-tooth gear A andhas a 12-tooth lower gear. A second compound gear C has a 60-tooth uppergear that engages the lower gear of the first compound gear B and has a12-tooth lower gear. A third compound gear D has a 60-tooth upper gearthat engages the lower gear of the second compound gear C and has alower 12-tooth gear. An 80-tooth gear E is fixed to the upper portion ofthe shaft 1062. The gear E engages the lower gear of the third compoundgear D.

The gear train 1320 provides an overall gear reduction of 833.33 (e.g.,5×5×5×6⅔). Thus, the shaft 1062 turns once for 833.33 revolutions of theoutput shaft of the motor 1300. However, since the shaft is fixed withrespect to the fixed support post 1040, the rotation of the motor shaftcauses the control head 1060 to rotate about the support post and thuscauses the mirror assembly (comprising the mirror support beam and theattached mirrors 1110, 1114, 1116) to rotate about the support post. Thelarge overall gear ratio of the gear train allows the relativelylow-powered motor to rotate mass of the control head at the mirrorassembly.

As further illustrated in FIGS. 15, 16 and 18, an upper portion of theshaft 1062 within the control head 1060 is constrained by a lower rollerbearing assembly 1350 and an upper roller bearing assembly 1052. Thelower roller bearing assembly is secured by the lower housing portion1070. The upper roller bearing assembly is secured within an openingformed in a support plate 1354. The support plate also includes aplurality of mounting extrusions 1356 to receive the upper ends of axlesthrough the compound gears B, C and D of the gear train 1320.

The upper end of the shaft 1062 is capped with a magnet housing 1360.The magnet housing secures a small bar magnet 1362, which has a northpole (indicated with a band for reference) and an opposing south pole.The poles are disposed in a horizontal plane. The circuit board 1310 ispositioned in the control head 1060 with an integrated 2-axis Hallsensor 1370 positioned directly over the bar magnet 1362. Thus, as thecontrol head is caused to rotate about the shaft by the motor 1300, theHall sensor is directly affected by the magnetic field produced by thebar magnet. In particular, the Hall sensor detects the absolute angularposition of the bar magnet. The Hall sensor is commercially available.In the illustrated embodiment, the Hall sensor comprises a 2SA-10Integrated 2-Axis Hall Sensor sold by Melexis Microelectronic Systems ofConcord, N.H.

After assembling the electrical and mechanical drive componentsdescribed above, the circuit board 1310 is positioned in the controlhead 1060. The circuit board is keyed to bosses on the lower portion1070 of the control head to assure that the circuit board is positionedwith the proper orientation. The connector 1306 that provides electricalpower to the motor 1300 via the conductors 1302, 1304 is plugged into afirst header 1400 on the circuit board. The connector 1312 that receivespower from the solar array 1200 via the conductors 1314,1316 is pluggedinto a second header 1402 on the circuit board.

FIG. 19 illustrates an embodiment of the circuitry 1500 that receivespower from the solar array 1200 and that drives the motor 1300 to directthe mirrors toward the sun. As discussed below, during normal operation,the circuitry is powered by the electrical energy generated by the solararray and includes a number of power saving features and fail-safe modesso that external power and control are not required after installation.

Primary power to the circuitry 1500 is provided by the solar array 1200as a variable voltage (VSOLAR_VAR) that is responsive to the intensityof the solar energy impinging on the solar array. The variable voltageis provided as an input to a power storage circuit 1510 that comprisesan input diode 1512 that prevents reverse current flow, and a zenerdiode 1514 in series with a series diode 1516. The zener diode and theseries diode 1516 are connected across a first super capacitor 1520 anda second super capacitor 1522, which are charged by the electricalcurrent from the solar array. The zener diode and the series diode limitthe voltage (VCAPS) across the super capacitors to approximately 10.7volts.

The super capacitors can also be charged from an external source (VEXT)via an external connector pin in a communications connector identifiedas Comm1, which will be discussed below. The external voltage is coupledto the VCAPS voltage via a Schottky diode 1532. In the illustratedembodiment, each of the super capacitors comprises a 1.0 farad capacitorsuch as, for example, FC Series super capacitors from NEC/Tokin. Thesuper capacitors are particularly advantageous because the supercapacitors have a high energy density compared to conventionalcapacitors. Unlike most rechargeable batteries, the super capacitors canbe charged and discharged hundreds of thousands of times with littledegradation. The super capacitors have high rates of charge anddischarge so that the super capacitors can be charged quickly duringperiods of intermittent sunlight and can provide bursts of energy, suchas, for example, when the motor 1300 is operated.

The voltage (VCAPS) across the super capacitors 1520, 1522 is providedto a buck power supply 1540. The buck power supply advantageouslycomprises a MAX1685 PWM Step-Down switching regulator from MaximIntegrated Products, Inc. The buck power supply is configured in aconventional manner with suitable resistor, inductors and capacitors(not shown) to receive an input voltage over a range of approximately2.75 volts to approximately 10.7 volts and to produce a substantiallyconstant output voltage of approximately 2.2 volts, which is identifiedas VMOTOR. The voltage VMOTOR is provided to a motor driver 1542, whichis described below.

The voltage VMOTOR produced by the buck power supply 1540 is alsoprovided as the input voltage to a boost power supply 1550. The boostpower supply is responsive to the input voltage to generate asubstantially constant output voltage of approximately 5.2 volts, whichis identified as VBOOST. The boost power supply advantageously comprisesa LM2623 step-up DC-DC switching regulator from National SemiconductorCorporation. The boost power supply is configured in a conventionalmanner with suitable resistor, inductors and capacitors (not shown).

The VBOOST voltage from the boost power supply 1550 is provided througha Schottky diode 1552 to a VDD node 1560. A super capacitor 1562 isconnected to the VDD node to store electrical energy that supplies acontrol processor 1600 and other circuitry when the boost power supply1550 is not active. In the illustrated embodiment, the super capacitorat the VDD node comprises a 0.1 microfarad capacitor available fromNEC/Tokin.

The VDD node 1560 is also connected via a Schottky diode 1570 to avoltage limiting zener diode 1572. The zener diode has a voltage ratingof approximately 5.1 volts and is connected to the solar array 1200 viaa Schottky diode 1574 and a resistor 1576. A filter capacitor 1578 ispositioned across the voltage limiting zener diode. The voltage(VSOL_LIM) across the zener diode and the capacitor provides analternative source of voltage to the Vdd node directly from the solarpanel 1200. During normal operations when the boost power supply 1550 isactive, the VBOOST voltage at the output of the boost power supply has ahigher voltage so that the limited voltage (VSOL_LIM) directly from thesolar array does not provide electrical energy to the node.

The buck power supply 1540 is selectively enabled by a Buck_Enablecontrol signal provided by a control processor 1600. The Buck_Enablesignal is coupled to an enable input of the buck power supply via afield effect transistor (FET) 1580, which has its source terminalconnected to ground and has its drain terminal connected to the Vcapsvoltage line via a pull-up resistor 1582. The FET is normally on so thatthe enable input of the buck power supply is grounded to prevent thebuck power supply from operating until the VDD voltage on the VDD node1560 is sufficiently high that a voltage supervisor 1610 (discussedbelow) releases a reset signal to enable the control processor tooperate. When the Buck_Enable signal is activated by the controlprocessor, the buck power supply is activated to produce the Vboostvoltage. By operating in this manner, the buck power supply does notconsume power while the super capacitors are charging after becomingsignificantly discharged (e.g., immediately after initial installationof the system).

The boost power supply 1550 is selectively enabled by a Boost_Enablecontrol signal provided by the control processor 1600. Since the boostpower supply receives power from the buck power supply 1540, the boostpower supply can only be enabled when the buck power supply is active.Thus, the Boost_Enable signal is supplied directly from the controlprocessor as shown. As discussed below, the control processor savespower by only enabling the power supplies when the energy is needed.Otherwise, the control processor is able to operate on stored energyfrom the super capacitor 1562 connected to the VDD node 1560.Accordingly, the energy stored in the larger super capacitors 1520, 1522is not drained when not needed.

The control processor 1600 advantageously comprises an ATmega166V 8-bitmicrocontroller available from Atmel Corporation. The control processoris responsive to an active reset signal generated by a voltagesupervisor circuit 1610 to reset to a known state and to begin operationfrom the known state when the reset signal is no longer active. Thevoltage supervisor monitors the voltage on the VDD node 1560 andgenerates a reset signal when the voltage decreases below 1.8 volts. Thevoltage supervisor circuit does not release the reset signal until thevoltage increases above 2.4 volts. The hysteresis provided by thevoltage supervisor circuit prevents the reset signal from switching onand off repeatedly as would happen if the voltage on the Vdd node variesabout a fixed threshold of a circuit without hysteresis. In theillustrated embodiment, the voltage supervisor circuit comprises anMAX6428MRUR-T single level battery monitor available from MaximIntegrated Products.

The reset signal to the control processor 1600 may also be generated ona connector pin of a COMM1 communication port or a COMM2 communicationport. The COMM1 port or the COMM2 port are used during installation andtesting and are not used during normal operation. For example, the COMM1port is a Serial Communication Interface (SCI) that operatesasynchronously in accordance with the RS232 protocol using theconventional TxD and RxD signals. The COMM2 port is a Serial PeripheralInterface (SPI) that operates synchronously using a master in/slave out(MISO) signal, a master out/slave in (MOSI) signal and a serial clock(SCK). In addition, each communication port includes a ground connectionand a connection that allows the Vdd voltage to be monitored.

The control processor 1600 is coupled to a real-time clock circuit 1620.The control processor and the real-time clock circuit communicate via aserial clock (SCK) signal generated by the control processor and abidirectional serial data (SDATA) signal. The real-time clock circuitadvantageously comprises a PCF8563 Real time clock/calendar integratedcircuit available from Philips Semiconductor.

The real-time clock circuit 1620 is programmed with the current date andtime and accurately tracks the time and date in response to timingprovided by a crystal 1622. The real-time clock circuit is primarilypowered from the Vdd voltage node 1560 via a Schottky diode 1624. Thereal-time clock circuit is also powered by a long-life battery 1626 viaa Schottky diode 1628. The battery advantageously comprises aconventional lithium battery having a voltage of, for example, 3.1volts. Since the battery voltage is lower than the voltage on the Vddvoltage node, the real-time clock circuit does not receive power fromthe battery unless the voltage on the Vdd voltage node drops below thebattery voltage. Accordingly, the battery can operate as a stand-bysource of electrical energy for the real-time clock circuit for manyyears without replacement.

The real-time clock circuit 1620 generates an interrupt signal that isprovided to the control processor 1600 to wake up the control processorso that the control processor is able to periodically confirm therotational positions of the mirrors and rotate the mirrors as needed todirect the mirrors toward the position of the sun as determined by thedate, time and location of the system. In particular, the controlprocessor sets an alarm time in the real-time clock circuit and thenenters a low power consumption mode until the real-time clock circuitactivates the interrupt signal to wake the control processor.

As discussed above, the system 1000 includes a 2-axis Hall sensor 1370that is responsive to the relative position of the Hall sensor on therotating circuit board 1310 (FIG. 16) with respect to the fixed magnet1362 on the end of the shaft 1062. (The relative rotation of the Hallsensor is represented pictorially by curved arrows in FIG. 19.) Therelative positions of the north and south poles of the magnet withrespect to the Hall sensor are sensed within the sensor. The Hall sensorproduces a first output signal VX and a second output signal VY, whichrepresent the X-coordinate and the Y-coordinate, respectively, of avector corresponding to the relative orientation of the magnet withrespect to the Hall sensor. The two output signals have voltage levelsthat are referenced to a reference signal identified as VCOM. The threesignals are provided to analog-to-digital interface of the controlprocessor 1600, which converts the analog signals to signed digitalvalues of X and Y. The control processor determines the current angle ofthe magnet with respect to the Hall sensor by calculating the arctangentof Y/X.

As discussed below, the Hall sensor 1370 is only accessed at certaintimes when the control processor 1600 is determining how much rotationis needed to direct the mirrors toward the current location of the sunor the anticipated location of the sun on a following day. Accordingly,the Hall sensor is only provided with power when needed. The Hall sensorreceives power from the VDD node 1560 via a PNP transistor 1630, whichis activated by an active low ENABLE_SENSOR signal from the controlprocessor. The PNP transistor provides a switched voltage (VSW) to thepower input of the Hall sensor.

As discussed above, the control processor 1600 controls the motor 1300via a motor driver circuit 1542. The motor driver receives a MOTOR1signal and a MOTOR2 signal from the control processor. When the MOTOR1signal is high and the MOTOR2 signal is low, the motor driver circuitprovides current to the motor in a first direction from an OUT1 terminalto an OUT2 terminal to cause the motor to rotate in a first direction(e.g., clockwise). When the MOTOR1 signal is low and the MOTOR2 signalis high, the motor driver circuit provides current to the motor in theopposite direction from the OUT2 terminal to the OUT1 terminal to causethe motor to operate in the opposite direction (e.g., counterclockwise).The motor driver circuit receives the VMOTOR voltage from the buck powersupply 1540 and receives the VDD voltage from the VDD node 1560. Thelower VMOTOR voltage is used to provide the current for driving themotor. The higher VDD voltage drives the logic circuitry within themotor driver circuit. Thus, the higher motor currents do not cause noiseon the VDD voltage used for the control processor and the other digitalcircuits.

As further illustrated in FIG. 19, an analog-to-digital input (A/D IN)of the control processor 1600 is connected to an output of an analogbuffer 1640. The analog buffer comprises an operational amplifier havingan input that is connected to receive the voltage (VCAPS) on the supercapacitors 1520, 1522. The control processor is able to monitor thevoltage on the super capacitors by converting the analog signal to adigital signal in an internal analog-to-digital converter. In preferredembodiments, the analog buffer has an input power connection coupled tothe VSW power connection of the Hall sensor 1370 so that the analogbuffer can be activated only when the control processor is reading thevalue of the super capacitor voltage.

In certain embodiments, the circuitry 1500 further includes a globalpositioning system (GPS) receiver 1650 mounted on the circuit board inthe control head 1060 and coupled to the control processor 1600 via aserial interface, such as, for example, the SCI interface via the R×Dand the T×D signal lines. The GPS receiver is selectively enabled by anENABLE_GPS signal line from the control processor. The GPS receiver mayalso have its power input connected to a switchable power supply (notshown) in a similar manner to the analog buffer 1640 and the Hall sensor1370. As discussed below, the GPS receiver can be accessed to obtainaccurate longitude and latitude information as well as accurate date andtime information.

FIGS. 20, 21 and 22 illustrate the operation of exemplary softwareroutines that perform the major functions that control the rotation andpositioning of the mirrors in the embodiment of FIGS. 12-19. Inparticular, FIG. 20 (comprising FIGS. 20A and 20B) illustrates a mainoperational routine 2000 that is executed when the control processor1600 is initially started from a reset condition. FIG. 21 (comprisingFIGS. 21A, 21B, 21C and 21D) illustrates a movement control routine 2200that is activated by the main operational routine. FIG. 22 illustratesthe setup power routine 2400 that is activated by the main operationalroutine.

As illustrated in FIG. 20A, when the main operational routine 2000begins, the control processor 1600 first turns off a watchdog timer inan activity block 2010. In an activity block 2012, the watchdog timer isset for 8 seconds. The watchdog timer is an internal logical structurewithin the control processor that counts the amount of time for which itis set. If the control processor is operating properly, the controlprocessor will execute an instruction that resets and restarts thewatchdog timer before the set time lapses. If the set time lapses beforethe watchdog timer is restarted, the watchdog timer generates aninternal interrupt to the control processor to cause the controlprocessor to execute a known routine to recover from an improperoperational condition.

Since the control processor 1600 has started from a reset condition, thestate of the control processor is unknown. In an activity block 2020,the control processor is initialized. In activity block 2022, the UART(SCI port interface) is initialized. In an activity block 2024, aninternal EEPROM is read to determine the current operational parametersof the control processor. In particular, the EEPROM stores thelongitude, the latitude and the south correction for a particularinstallation. The EEPROM also stores a default interval time to use tocontrol the movement of the system during the daytime. For example, in apreferred embodiment, the default interval time is 5 minutes. The EEPROMis advantageously preprogrammed with the values before shipping thesystem for installation. The EEPROM may also store additional parametersthat may be used for testing and identification of the system, but whichare not pertinent to the operation of the system as described herein.

In an activity block 2030, the control processor 1600 activates aninternal USART to activate the SCI interface to the asynchronous serialport (COMM1) and then sends data out on the serial port via the SCIinterface in an activity block 2040. The control processor activates theasynchronous serial port in case the control processor is being poweredup for initial installation or for maintenance, in which case anexternal system may be coupled to the SCI interface to communicate withthe control processor.

In an activity block 2042, the control processor 1600 waits one second.Then, in a decision block 2044, the control processor determines whetherany serial data was received via the serial port. If serial data hasbeen received, the control processor is connected with an externalsystem. Accordingly, the control processor advances to an activity block2050 and sets an internal MODE status flag to SETUP_MODE. Then, thecontrol processor advances to a Set Targets activity block 2094 (FIG.20B).

If no serial data has been received when checked in the decision block2044, the control processor 1600 determines in a decision block 2054whether three attempts to check for serial input data have beencompleted. If three attempts have not been completed, the controlprocessor returns to the activity block 2042 and waits another second.If three attempts have been made without receiving serial data, thecontrol processor advances from the decision block 2054 to an activityblock 2070 (FIG. 20B).

In the activity block 2070, the control processor 1600 sets the targetvalues. Basically, the control processor reads the real-time clock 1620to determine the current year, month, day, hour and minute to be used inthe position calculations.

After setting the target values, the control processor 1600 sets theMODE to RUN_MODE in activity block 2072 and then proceeds to an activityblock 2074. In the activity block 2074, the control processordeactivates the USART since the USART is not used during normaloperations. The control processor then sets a GO_RECEIVED status flag toTRUE to indicate that the control processor is to control the movementof the control head 1060. After setting the GO_RECEIVED status flag, thecontrol processor advances to an activity block 2080. In the activityblock 2080, the control processor reads the voltage (VCAPS) on the mainsuper capacitors 1520, 1522 (FIG. 19) via the analog buffers 2040. In adecision block 2082, the control processor determines whether the supercapacitor voltage is at least 7 volts. If the super capacitor voltage isat least 7 volts, the control process advances to the activity block2094 and sets the target values (e.g., the date and time), as discussedabove.

After setting the target values, the control processor 1600 advances toan activity block 2096 and turns the buck power supply 1540 and theboost power supply 1550 off by turning off the BUCK_ENABLE signal andthe BOOST_ENABLE signals, respectively. The two supplies are only neededto generate energy to move the motors and are not turned on until thecontrol processor determines that movement is required.

After turning off the supplies, the control processor 1600 advances toan activity block 2100 and resets the watchdog timer. The controlprocessor then advances to an activity block 2102 to execute themovement control routine 2200 illustrated in FIG. 21. When the controlprocessor returns from the movement control routine, the controlprocessor returns to the activity block 2100 to again reset the watchdogtimer. The control processor remains in this loop until reset by anexternal system or by the detection of a low voltage by the voltagesupervisor 1610. The control processor may also exit the loop if thewatchdog timer times out.

If the control processor 1600 determines in the decision block 2082 thatthe super capacitor voltage (VCAPS) is less than 7 volts, the controlprocessor advances to an activity block 2110 to add 10 minutes to thetarget wakeup time. The control processor then sets the target values inan activity block 2112 to set the updated target values. In an activityblock 2114, the control processor normalizes the time to assure that thetime is in the proper format to send to the real-time clock 1620 andtransfers the wakeup time to the real-time clock. In particular, thenormalize time routine assures that the time is correct when theincrement in the target wakeup time rolls over to a new day, month oryear. The normalize time routine also handles the adjustments for thenumber of days in each month including the adjustment for leap years.The control processor then powers down in an activity block 2116 untilreceiving an interrupt from the real-time clock when the wakeup timeoccurs. When powering down in this mode, the control processor retains acurrent state so that the control processor returns to the same stateupon receiving the interrupt from the real-time clock. The power downactivity block 2116 includes a step of disabling the watchdog timer sothat the watchdog timer does not detect a fault caused by inactivity ofthe control processor while powered down.

The steps of reading the super capacitor voltage and selectivelydelaying for an additional 10 minutes are included to accommodate asystem that has not been installed for a considerable time after thesuper capacitors are initially charged after manufacturing. If thevoltage on the super capacitors is too low when initially installed, theelectrical power from the solar array panel 1200 will quickly charge thesuper capacitors 1520, 1522 while the control processor 1600 is powereddown. When the voltage is at least 7 volts, the control processor willexecute the activity block 2090 and the subsequent steps.

FIG. 21 (comprising FIGS. 21A, 21B, 21C and 21D) illustrates themovement control routine 2200 that is called by the main routine 2000.In an activity block 2210, the control processor 1600 sets the targetvalues to update the target values with any recent calculations. In anactivity block 2212, the control processor sets an internal valuerepresenting a MOVES counter to an initial value of 0. The controlprocessor then resets the watchdog timer in activity block 2214 to starta new 8-second count. The control processor sets the MOVES counter toMOVES+1 in an activity block 2216.

In an activity block 2220, the control processor 1600 reads the digitalvalue on the analog-to-digital converters connected to receive the VX,VY and VCOM values from the Hall sensor 1370. In order to access theHall sensor, the control processor temporarily activates theENABLE_SENSOR signal to turn on the PNP transistor 1630 to provide powerto the Hall sensor. After reading the sensor values, the controlprocessor calculates the current Hall sensor angle using the new valuesin an activity block 2222. In an activity block 2224, the controlprocessor calculates a current absolute angular position of the controlhead 1060 based on the current Hall sensor value and the savedparameters based on the orientation of the horizontal support beam 1032.In the illustrated embodiment, the control processor also includes anoffset for the angular position of the circuit board 1310 within thecontrol head. Accordingly, the current absolute angular positionaccurately represents the geographic direction towards which the mirrorsare currently pointing.

In an activity block 2230, the control processor 1600 initially sets aninternal MOVE_DIRECTION parameter to CCW to indicate the usual directionof movement of the control head 1060. In an activity block 2232, thecontrol processor calculates the sun azimuth in accordance with currentdate and time read from the real-time clock 1620 and in accordance withthe latitude and longitude values that were stored at the time ofinstallation. In an alternative embodiment, the latitude and longitudevalues as well as the current time may be obtained from the optionalglobal positioning system (GPS) 1650 included as part of the electroniccircuitry on the circuit board 1310. In particular, the GPS may beaccessed once after a reset condition to establish the position of thesolar tracking system 1000 for a new installation or after the solartracking system has lost power (for example, after being uninstalled andrepositioned at a new location). The GPS may also be accessedperiodically (e.g., once per day) to verify and update the date and timeprovided by the real-time clock.

After calculating the sun azimuth, the control processor 1600 advancesto a decision block 2234 and determines whether a calculated sunaltitude is less than 0 thereby determining whether the sun is below thehorizon at the current position at the current time. If the sun altitudeis less than 0, the control processor sets an IN_DARKNESS parameter inan activity block 2236. Then, in an activity block 2238, the controlprocessor calculates the time of the next sunrise and calculates the sunazimuth at the calculated sunrise time. The control processor thenadvances to an activity block 2240 (FIG. 21A). If the sun altitude is atleast 0, the control processor advances directly to the activity block2240 without setting the IN_DARKNESS parameter.

In the activity block 2240, the control processor 1600 sets aTARGET_ANGLE parameter to the calculated azimuth angle. The controlprocessor then advances to a decision block 2242 to compare the currentmeasured angular position with the calculated TARGET_ANGLE. If thecurrent angular position is equal to the TARGET_ANGLE, the mirrors arecurrently pointed toward the sun and no movement is necessary. Thecontrol processor advances directly to a decision block 2250 (FIG. 21D),which is discussed below. If the current angle is not equal to theTARGET_ANGLE, the control processor advances to an activity block 2262to calculate an AMOUNT equal to the TARGET_ANGLE minus theCURRENT_ANGLE. The AMOUNT is a calculated adjustment in degrees. Sincethe calculation can result in an adjustment less than 0 degrees orgreater than 360 degrees, the processor executes an activity block 2264to convert an AMOUNT less than 0 to an amount between 0 and 360 byadding 360 and executes an activity block 2266 to convert an AMOUNTgreater than 360 to an amount between 0 and 360 by subtracting 360. Onlyone of the activity blocks 2264 and 2266 may be executed if the AMOUNTis outside the range of 0 to 360. If the AMOUNT is between 0 and 360,neither activity block is executed.

After performing any required calculation in the activity block 2264 orthe activity block 2266, the control processor 1600 advances to adecision block 2270 to determine whether the calculated AMOUNT is atleast as great as 180 degrees. If the amount is at least 180 degrees,the control processor advances to an activity block 2272 and sets theMOVE_DIRECTION parameter to counterclockwise (CCW). The controlprocessor then advances to an activity block 2274 (FIG. 21C) where thecontrol processor subtracts the amount from 360. Basically, the controlprocessor is calculating a small rotational amount in thecounterclockwise direction when the calculated amount in the clockwisedirection is greater than or equal to 180 degrees. The control processorthan advances to a decision block 2280.

If the calculated AMOUNT is less than 180 degrees, the control processor1600 advances from the decision block 2270 to an activity block 2276where the control processor sets the MOVE_DIRECTION parameter toclockwise (CW). The control processor advances from the activity block2276 directly to the decision block 2280.

In the decision block 2280, the control processor 1600 tests whether theAMOUNT is greater than 6. If the AMOUNT is greater than 6, the controlprocessor advances to a decision block 2282 and determines whether theIN_DARKNESS parameter is TRUE. If the IN_DARKNESS parameter is not set,the control processor sets the AMOUNT to a maximum value of 6 in anactivity block 2284 and then advances to a decision block 2286. If theIN_DARKNESS parameter is set, the control processor advances directly tothe decision block 2286 without adjusting the value of the AMOUNT. Ifthe control processor determines that the AMOUNT is no more than 6, thecontrol processor advances directly from the decision block 2280 to thedecision block 2286. As discussed below, the AMOUNT NT represents theangular amount of rotation allowed per motor operation. During thedaytime, the AMOUNT is limited to 6 degrees. At night, the AMOUNT can begreater than 6 so that the mirrors can be quickly rotated to acalculated position for the next morning.

In the decision block 2286, the control processor 1600 determineswhether the current value of the MOVES parameter is equal to 1. If theMOVES parameter is equal to 1, the control processor advances to adecision block 2288 and again tests whether the IN_DARKNESS parameter isTRUE. If the IN_DARKNESSparameter is not True, the control processoradvances to an activity block 2290 (FIG. 21D) and multiplies the AMOUNTtimes 1.5 to cause the first daytime move in a move sequence to begreater than the subsequent moves. The control processor then advancesto a decision block 2292.

If the IN_DARKNESS parameter is TRUE in the decision block 2288 or ifthe MOVES count is not equal to 1 in the decision block 2286, thecontrol processor 1600 bypasses the activity block 2290 and advancesdirectly to the decision block 2292.

In the decision block 2292, the control processor 1600 determineswhether the AMOUNT is greater than 1. If the AMOUNT is not greater than1, the control processor advances to the decision block 2250, which isdiscussed below.

If the AMOUNT is greater than 1, the control processor 1600 advancesfrom the decision block 2292 to an activity block 2300. In the activityblock 2300, the control processor activates the buck power supply 1540to generate the Vmotor voltage for the motor driver circuit 1542 andactivates the boost power supply 1550 so that the voltage on the VDDnode 1560 is provided with a consistent source of DC power derived fromthe energy stored in the main super capacitors 1520, 1522 during themotor operation. During times when the motor is not operating, the Vddvoltage stored on the small super capacitor 1562 at the VDD node issufficient to operate the digital circuits, and the buck power supplyand the boost power supply are not needed during those times.

In the activity block 2300, the control processor 1600 sends signals tothe motor driver circuit 1542 to activate the motor 1300 for an amountof time corresponding to the calculated and adjusted AMOUNT. After themotor movement is completed, the control processor turns off the buckpower supply 1540 and the boost power supply 1550. Thereafter, thecontrol processor returns to the activity block 2214 (FIG. 21A) andrepeats the process just described until the control processor advancesto the decision block 2250 when the AMOUNT is no greater than 1(decision block 2290) or the CURRENT_ANGLE is equal to the TARGET_ANGLE(decision block 2242 in FIG. 21B).

As discussed above, the control processor 1600 advances to the decisionblock 2250 from the decision block 2242 (FIG. 21B) when theCURRENT_ANGLE is equal to the TARGET_ANGLE or from the decision block2292 when the AMOUNT is not greater than 1. In either of the two cases,no movement is to be performed during the current pass through themovement control routine 2200. In the decision block 2250, the controlprocessor determines whether the IN_DARKNESS status flag is TRUE. If theIN_DARKNESS status flag is not TRUE when tested in the decision block2250, the control processor advances to an activity block 2310 and addsthe interval time (e.g., 5 minutes in the illustrated embodiment) to theprevious alarm time so that the control processor will be awakened againin 5 minutes. The control processor than advances to an activity block2312. If the IN_DARKNESS status flag is TRUE, the control processoradvances directly to an activity block 2312 from the decision block 2310without adjusting the alarm time, which has already been calculated forthe time of the next sunrise.

In the activity block 2312, the control processor normalizes the wakeuptime and transfers the wakeup time to the real-time clock 1620 as analarm value. The control processor then advances to an activity block2314 where the control processor turns off any unnecessary power andceases activity until the control processor receives an interrupt fromthe real-time clock at the designated alarm time. The control processoralso disables the watchdog timer during this time so that the watchdogtimer does not reset the control processor during this portion of thenormal operation of the control processor. The activities to power downuntil the next alarm is received are illustrated in FIG. 22, describedbelow.

During the daytime, the alarm time is advantageously set to a selectedtime after the current time. For example, in one embodiment, the alarmtime is set for five minutes after the current time so that controlprocessor 1600 wakes up every five minutes to determine how far torotate the control head in order to direct the mirrors toward the sun.In alternative embodiments, the interval for the alarm times may bevaried. For example, during the early morning hours and late eveninghours during the summer, the elevation of the sun may change rapidlywithout significant changes in the azimuthal position. Thus, the controlprocessor may be awakened less often. During the middle of the daytimehours, the azimuthal position changes more rapidly, and the controlprocessor may use a smaller interval between wakeup times. After the sunsets, the mirrors are quickly rotated to the calculated azimuthalposition of the sun for the following morning, and the wakeup alarm isset for a calculated time after sunrise.

When the wakeup time occurs and the real-time clock 1620 interrupts thecontrol processor 1600, the control processor executes an activity block2320 in which the control processor reads the internal EEPROM toretrieve the longitude and latitude values and the south correctionvalue. The control processor also re-enables the watchdog timer. Thecontrol processor then advances to a decision block 2322 and determineswhether the IN_DARKNESS status flag is set to TRUE. If the IN_DARKNESSstatus flag is TRUE, the control processor is being awakened afterpowering down for the night; otherwise, the control processor is beingawakened following a prior movement during the daytime.

If the IN_DARKNESS status flag is TRUE, the control processor 1600advances from the decision block 2322 to an activity block 2330 wherethe control processor sets the TARGET values and then advances to anactivity block 2332 where the control processor sets the IN_DARKNESSstatus flag to False. The control processor than exits the movementcontrol routine and returns to the main routine in FIG. 20B.

FIG. 22 illustrates the power down routine 2400 that is activated by thecontrol processor 1600 from the activity block 2314 in FIG. 21D and alsofrom the activity block 2116 in FIG. 20B. In the power down routine, thecontrol processor turns off all unnecessary power and then shuts itselfdown in a sleep mode until awakened by an alarm interrupt from thereal-time clock 1620. During the sleep mode, the control processorconsumes minimal power.

The power down routine 2400 starts in activity block 2410 where thecontrol processor 1600 sets the alarm day and time using the normalizeddate and time values calculated in the previously described steps. Then,in an activity block 2412, the control processor shuts down anyunnecessary devices including the buck power supply 1540, the boostpower supply 1550, the Hall sensor 1370, analog buffer 1640, and anyinternally switchable devices, such as, the communications interfacesdescribed above.

After shutting down the unnecessary devices, the control processor 1600advances to an activity block 2420 and resets any previously receivedinterrupt so that an interrupt will not be present when the controlprocessor enables interrupts in the next step. The control processorthen advances to an activity block 2422 and enables interrupts. Thecontrol processor then enables the processor sleep mode in an activityblock 2424. In particular, the control processor selects a mode in whichall non-essential processes will be stopped including instructionoperation. After selecting the sleep mode, the control processordisables the watchdog timer so that the watchdog timer will not generatean interrupt only a few seconds after the control processor stopsexecuting instructions.

After setting up the system for sleeping in the previous blocks, thecontrol processor 1600 advances to an activity block 2440 where thecontrol processor executes the instruction that causes the controlprocessor to enter the selected sleep mode. When the instruction isexecuted, all further instruction execution stops. The instructioncounter within the control processor is set to the next instruction tobe executed when the control processor receives the wakeup alarminterrupt from the real-time clock 1620. The control processor remainsin the sleep state for as little as five minutes during the daytime. Theduration of the sleep state during the night will vary in accordancewith the time of year and the latitude at which the system is installed.

When the real-time clock 1620 reaches the date and time set for thealarm, the real-time clock activates the hardware interrupt to thecontrol processor 1600, as represented by a block 2450. Interrupthandling hardware within the control processor responds to the hardwareinterrupt by activating the instruction execution logic within thecontrol processor, which causes the control processor to execute theinstruction following the sleep instruction in the activity block 2440.In particular, the control processor wakes up and resumes instructionexecution in an activity block 2460. The control processor firstdisables the processor sleep mode in an activity block 2470 so that anyinadvertent execution of a go to sleep instruction cannot cause thecontrol processor to go to sleep until the real-time clock has beenprogrammed with a new alarm date and time subsequent to the current dateand time. The control processor than enables the watchdog timer in anactivity block 2472 and returns to the routine that called the powerdown routine 2400. For example, if the power down routine was called bythe activity block 2314 in FIG. 21D, the control processor returns tothe activity block 2320 and performs the functions described above.

As described above, the solar tracking unit is self-powered from solarenergy and includes power saving features that allow the unit to operatefor many years without requiring external communications and withoutrequiring an external source of energy. In particular, the controlprocessor 1600 is programmed to shut down all unnecessary devices untilneeded to move the control head or to measure the current angularposition of the control head. By implementing the power savingfunctions, the system is able to operate by relying solely on the solararray 1200 to maintain the super capacitors in a charged condition.

One skilled in art will appreciate that the foregoing embodiments areillustrative of the present invention. The present invention can beadvantageously incorporated into alternative embodiments while remainingwithin the spirit and scope of the present invention, as defined by theappended claims.

1. A solar tracking system mountable above a skylight of a building,comprising: a control box; an electrical motor within the control boxthat drives the control box about a shaft that extends below the controlbox; a vertical support structure positionable above a central portionof the skylight, the vertical support structure having an upper portionthat receives the shaft extending from the control box; a motion controlcircuit within the control box that controls the motor to cause thecontrol box to rotate about the extended shaft; a voltage supply circuitwithin the control box to provide electrical energy to the motioncontrol circuit and the motor; a solar array mechanically andelectrically coupled to the control box, the solar array producingelectrical energy in response to sunlight and providing the electricalenergy to the voltage supply circuit within the control box sufficientto operate the control box without any other source of electricalenergy; and a mirror support structure coupled to the control box torotate with the control box, the mirror support structure supporting atleast one mirror positioned at an angle to reflect sunlight through theskylight into the building.
 2. The solar tracking system as defined inclaim 1, wherein the motion control circuit intermittently rotates thecontrol box during daytime hours to position the at least one mirrortowards calculated positions of the sun, and wherein the motion controlcircuit rotates the control box at the end of a day to a calculatedposition of the sun at sunrise on the next following day.
 3. The solartracking system as defined in claim 2, wherein the motion controlcircuit calculates the position of the azimuthal position of the sunbased on the date and time of day and based on at least the latitude andlongitude position of the solar tracking system.
 4. The solar trackingsystem as defined in claim 3, wherein the latitude and longitudeposition are permanently stored in a non-volatile memory within themotion control circuitry.
 5. The solar tracking system as defined inclaim 3, wherein the latitude and longitude position and the date andtime of day are obtained by accessing a global positioning receiverincorporated into the motion control circuitry.
 6. The solar trackingsystem as defined in claim 1, wherein the voltage supply circuitcomprises: a first voltage generating circuit comprising passivecomponents coupled to the electrical output of the solar array, thefirst voltage generating circuit charging at least a first storagecapacitor to a variable voltage, the variable voltage across the storagecapacitor limited to a maximum value by a first voltage limiting device;a second voltage generating circuit comprising passive componentscoupled to the electrical output of the solar array, the second voltagegenerating circuit comprising a second voltage limiting device toprovide a limited output voltage, the limited output voltage provided toa common voltage node, the common node being coupled to the power inputterminals of digital devices in the motion control circuit; a thirdvoltage generating circuit comprising a buck power supply coupled toreceive the variable voltage from the first voltage circuit, the buckpower supply producing a first constant voltage when enabled by themotion control circuit, the first constant voltage provided as a powersource for the electrical motor; a fourth voltage generating circuitcomprising a boost power supply coupled to receive the first constantvoltage, the boost power supply producing a second constant voltage whenenabled by the motion control unit, the second constant voltage providedto the common voltage node such the voltage at the common voltage nodeis the higher of the limited output voltage from the second voltagegenerating circuit or the second constant voltage; and a second storagecapacitor coupled to the common voltage node to be charged by the higherof the limited output voltage from the second voltage generating circuitor the second constant voltage from the fourth voltage generatingcircuit, and supply electrical energy to the common voltage node whenthe limited output voltage and the second constant voltage are both lessthan the voltage across the second storage capacitor.
 7. The solartracking system of as defined in claim 6, wherein the buck power supplyis selectively enabled by an enable signal from the motion controlcircuit, and wherein the enable signal is maintained in an inactivestate until the motion control circuit receives a sufficient voltagefrom the first voltage generating circuit to be fully operational. 8.The solar tracking system as defined in claim 1, wherein the firststorage capacitor is a super capacitor.
 9. The solar tracking system asdefined in claim 8, the first storage capacitor has a capacitance of atleast 1 farad.
 10. The solar tracking system as defined in claim 1,wherein the second storage capacitor is a super capacitor.
 11. A solartracking system mountable above a skylight of a building, comprising: acontrol box; a motor assembly within the control box, the motor assemblyincluding a motor shaft that extends below the control box; a verticalsupport structure positionable above a central portion of the skylight,the vertical support structure having an upper portion coupled to themotor shaft to position the control box above the upper portion; controlcircuitry within the control box that controls the motor to cause thecontrol box to rotate about the motor shaft approximately once per day;an energy storage device within the control box to provide electricalenergy to the control circuitry and to the motor assembly; a solar arraymechanically and electrically coupled to the control box, the solararray producing electrical energy in response to sunlight and providingthe only source of electrical energy to recharge the energy storagedevice; and a mirror support structure coupled to the control box torotate with the control box, the mirror support structure supporting atleast one mirror positioned at an angle to reflect sunlight through theskylight into the building.
 12. The solar tracking system as defined inclaim 11, wherein: the control box has an outer wall, which ispenetrated by at least first and second openings located at respectivefirst and second angular positions with respect to an axis of rotationof the motor shaft, each opening admitting a respective beam of sunlightinto the control box when the respective opening is facing in adirection generally toward the sun; the control box includes at leastone photodetector, the photodetector located in the control box at anangular position between the first and second angular positions of thefirst and second openings, so that the photodetector is in a shadedposition between the beams of sunlight admitted through the first andsecond openings unless the control box rotates to a position to allowthe beam of sunlight admitted through one of the first and secondopenings to impinge upon the photodetector; and the control circuitry isresponsive to the electrical signal from the photodetector to adjust theangular position of the control box to cause the photodetector to beshaded from the sun between the beams of sunlight from the first andsecond openings.
 13. The solar tracking system as defined in claim 12,wherein the solar array and the at least one mirror face the sun whenthe photodetector is shaded from sunlight passing through either of thetwo openings.
 14. The solar tracking system as defined in claim 12,wherein the photodetector is inactive when the photodetector is shadedfrom the beams of sunlight passing through the two openings.
 15. Thesolar tracking system as defined in claim 12, wherein the controlcircuitry is responsive to an active signal from the photodetector toautomatically determine which opening is admitting sunlight impinging onthe photodetector and to position the control box so that thephotodetector is positioned in the shade between the beams of sunlightfrom the first and second openings.
 16. The solar tracking system asdefined in claim 12, wherein the control circuitry automatically adaptsto a new installation to rotate the control box until the photodetectordetects sunlight through one of the openings and to then rotate thecontrol box until the photodetector detects sunlight through the otheropening, the control circuitry responsive to the direction of rotationwhen the photodetector detects sunlight through the other opening todetermine whether the solar tracking system is located in the northernhemisphere or the southern hemisphere, the control circuitry setting thedirection of rotation of the control box in accordance with the locationof the solar tracking system.